The present invention relates generally to printing on sheet-type work materials using inkjet, dot matrix, thermal, or like print heads, and deals more particularly with an apparatus and method for printing on a continuously fed sheet of work material.
The present invention is directed to an apparatus and method for printing a graphic onto a continuously moving sheet of work material, and will be described herein as applied to such use.
In known printers, a single print head is usually mounted on a frame for movement transversely across a piece of sheet-type work material. In many instances the print head includes a print cartridge having an ink reservoir and a number of discrete inkjets arranged in a matrix-like pattern adjacent to the media to be printed. This matrix-like pattern of inkjets is referred to by those skilled in the pertinent art as an array.
Typically, a line of a graphic is printed onto the work material by causing the print head to traverse the work material while the work material is stationary. As the print head moves, the inkjets spray appropriately colored ink onto the work material in accordance with commands issued from a controller. The work material is then incrementally advanced an amount preferably equal to the height of the array of inkjets, and the print head makes another pass across the work material. This process of incrementally advancing the work material and printing, is continued until the entire graphic is printed thereon.
A problem associated with printing in the above-described manner is that the incremental indexing of the work material causes the printing process to be very time consuming, and therefore expensive. In addition, in large printing applications, it is often necessary to accelerate and decelerate large rolls of sheet material whose inertia can make accurate indexing difficult.
Moreover, the discrete motion of the work material can cause slight misalignments therein, that in turn generate inaccuracies in the printed graphic. In addition, after a line is printed the work material must be advanced an amount equivalent to the height of the array of inkjets defined by the print cartridge. Any deviation will either cause overlap or gaps between successive printed lines depending on whether the work material is advanced too far or too little.
Based on the foregoing, it is the general object of the present invention to provide a printing apparatus that overcomes the above-described problems and drawbacks present in the prior art.
It is a more specific object of the present invention to provide a printing apparatus that can print a graphic onto a piece of sheet-type work material while the material is continuously advanced through the printing apparatus.
The present invention is directed to an apparatus for printing on a continuously moving sheet of work material that includes a frame defining a work supporting surface, as well as means for continuously feeding the work material in a first coordinate direction longitudinal of itself, over the work supporting surface. An elongated support having first and second ends is coupled to the frame and extends transversely across the work supporting surface with at least one print head coupled to the support for movement between the first and second ends.
In an embodiment of the present invention, means are provided for selectively and continuously moving the print head across the elongated support between the first and second ends. A controller having graphical data stored therein in machine readable format is in communication with the printing apparatus and the print head. During operation, and in response to commands issued from the controller, the combined motion of the print head and the work material relative to one another, causes successive lineal portions of the graphic to be transferred onto the work material and be oriented approximately perpendicular to the first coordinate direction.
Preferably, the print head includes a plurality of spaced-apart rows of discrete print elements, such as ink jets arranged in a matrix-like array having a given height. During operation, when the print head reaches either the first or second end of the elongated support, the above-described means for progressively moving the print head cause it to move in a direction opposite to the first coordinate direction, an amount equal to the width of the printed line less the distance moved by the work material during this print head motion.
In another embodiment of the present invention, a portion of the array of print elements is selectively actuated, allowing the actuated portions of the array to shift along the first coordinate direction as the print head traverses the advancing sheet material. Accordingly, the shifting portions of the array of print elements in combination with the motion of the material in the first coordinate direction cause the print head to print a lineal portion of a graphic onto the work material.
The means for selectively and continuously moving the print head between the first and second ends of the elongated support, can take the form of a belt mounted on a pair of sprockets that in turn are rotatably mounted to the support. One sprocket in the pair is located adjacent to the first end of the support, and the other sprocket in the pair is located adjacent to the second end of the support.
Alternatively, the belt can be mounted at an angle relative to the work material, thereby eliminating the need for the print to move between the above-described retracted and extended positions.
In another embodiment of the present invention, the elongated support is pivotally coupled to the frame for selective movement between first and second angles. Preferably, the second angle is approximately equal and opposite to the first angle. In operation, the print head is slidably coupled to, and moves along the support between the first and second ends. The support pivots between the first and second angles in response to commands issued from the controller, enabling the print head to continuously print successive lineal portions of a graphic onto the work material and oriented approximately perpendicular to the first coordinate direction.
In still another embodiment of the present invention, the path traversed by the print head is figure-8-shaped and is defined by a path coupled to an underside of the elongated support. The path includes a first segment oriented along a first angle and a second segment oriented along a second angle approximately equal and opposite to the first angle. Preferably, the second segment crosses the first segment at a point approximately midway across the work material being fed through the apparatus.
In addition to the foregoing, the present invention can also employ a plurality of staggered print heads, slidably coupled to the elongated support and spaced a predetermined distance away from the next successive print head. During operation, each of the print heads prints a lineal portion of the graphic along a line approximately perpendicular to the first coordinate direction as the print head traverses a respective one of the first and second segments, thereby printing several lines in a single pass.
The present invention also resides in a method for printing a graphic onto a continuously moving sheet of work material whereby an apparatus as described above is provided. The work material is moved through the apparatus in the first coordinate direction, at a predetermined rate. The print head, in response to commands issued from the controller traverses the elongated support between the first and second ends. Concomitant with this movement, the print head is also moved between the forward and rearward positions, such that the movement of the print head has a component of speed in the first coordinate direction approximately equal to the rate at which the work material is being advanced. While the print head is being moved, a lineal portion of a graphic is printed onto the work material and is oriented approximately perpendicular to the first coordinate direction.
Upon reaching either of the first or second ends, the print head is moved in a direction opposite to the first coordinate direction an amount approximately equal to the width of the printed line, less the distance the work material was advanced during the print head""s motion the print is then moved back across the work material.